The US Food and Drug Administration (FDA) now has regulatory authority over tobacco, including the selection and changing of pictorial and textual content for health warning labels (HWLs) on cigarette packaging. In September 2012, the US is scheduled to implement nine different text messages and images on HWLs that will cover 50% of the front and back of cigarette packs. After the first round of pictorial HWLs is implemented, its effects will wear out over time. The FDA is charged with changing the content of HWLs if they have evidence that changing them will ...promote greater public understanding of the risks associated with the use of tobacco products.'' The proposed study will address methodological shortfalls of previous studies to provide researchers and US regulators with state-of-the-art scientific evidence on the effects of key pictorial HWL policy characteristics on smokers' understanding of smoking-related risks and on smoking cessation. The results will inform legal challenges to implementation of current US policy, and they will provide the basis for decision-making about future pictorial HWL policy in the US and around the world. We propose to conduct studies of adult smokers in the US and in three comparable countries that will all implement new pictorial HWLs in 2012, but with policies that differ from one another in important ways: 1. the US will implement its 1st round of pictorial HWLs, using short and simple risk messages; 2. Mexico will rotate new HWLs at the highest frequency in the world (i.e., two new HWLs every three months); 2. Canada will implement its 2nd round of pictorial HWLs, which include comprehensive risk and quit messages; 4. Australia will implement its 2nd round of pictorial HWLs, while also implementing the innovative policy of prohibiting brand colors and logos from cigarette packages in order to enhance the efficacy of HWLs. This project will capitalize on the unprecedented opportunity to systematically examine the real world effects over time of different pictorial HWL policies that US regulators should consider for future policy development. The proposed project will pursue the following specific aims: Specific Aim 1: We will use a quasi-experimental design with panels of adult smokers in four countries (Canada, Australia, Mexico, United States) to determine which pictorial HWL characteristics most effectively promote understanding of smoking-related risks and increase cessation behavior. Specific Aim 2: We will conduct a series of controlled randomized experiments among adult smokers in the same four countries, systematically varying their exposure to pictorial HWL characteristics that are novel relative to existing HWLs, in order to determine the cognitive and affective impact of these manipulations. Meeting these aims will produce the scientific evidence that US regulators need on the real world impacts of different pictorial HWL policy options. Results will be disseminated to researchers and decision-makers, including the FDA, which can revise US HWLs to improve consumer understanding of smoking-related harms.